Geochemistry and petrogenesis of the East Branch Brook metagabbroic dykes in the Sawyer Brook fault zone, Clarence Stream gold prospect, southwestern New Brunswick

Authors

  • Kathleen G. Thorne Department of Geology. University of New Brunswick, PO Box 4400. Fredericton. NB E3B 5A3 *Current address: New Brunswick Department of Natural Resources and Energy. Geological Surveys Branch. P.O. Box 6000. Fredericton. NB F3B 5111
  • David R. Lentz Department of Geology. University of New Brunswick, PO Box 4400. Fredericton. NB E3B 5A3 *Current address: New Brunswick Department of Natural Resources and Energy. Geological Surveys Branch. P.O. Box 6000. Fredericton. NB F3B 5111

DOI:

https://doi.org/10.4138/1978

Abstract

The East Branch Brook (EBB) metagabbroic dykes, host to a portion of the Clarence Stream gold deposit, are situated within the contact metamorphic aureole of the Middle Devonian I-type Magaguadavic Granite on the northwestern margin of the post-orogenic Saint George Bathohth. They are highly deformed, light- (type I), intermediate- (type 2) to dark-coloured (type 3) dykes containing auriferous quartz veins that occupy brittle to ductile northeast-trending shear zones in shallow marine, hornfelsed, volcaniclastic, sedimentary rocks of the Silurian Waweig and Oak Bay formations. The shear zones parallel the regional structure as a result of proximity to the faulted boundary (Sawyer Brook fault) between the Ordovician St. Croix terrane to the northwest and the Silurian to Early Devonian Mascarcne Basin to the southeast. Geochemical studies of the EBB dykes indicate that three pulses (Fe-rich. intermediate, and Mg-rich) of subalkaline to slightly alkaline continental tholeiitc magmas were generated in a transpressional environment during the Early Silurian to Early Devonian Positive εNd values indicate their derivation from a partially depleted mantle source during faulting and nft-related events Although the geochemical data (Fe- and Ti-depletion) indicate calc-alkaline affinity for the nearby Bocabec intrusive complex, εNd values and primitive mantle-normalized spider diagram patterns are similar to those of the EBB dykes. In contrast, the St. Stephen Intrusion appears more primitive with within-plate tholeiitic to slightly alkalie affinity RÉSUMÉ Les dykes metagabbroïques du ruisseau East Branch, qui abritent une partie du gite aurifière dc Clarence Stream, sont situées à l'inténeur de 1'auréolc de métamorphismc de contact du granite du Dévonian moyen de type 1 de Magaguadavic sur la limite nord-ouest du batholithe postorogénique de Saint George. Il s'agit de dykes extrémemeni déformés de teinte pàle (type 1) et intermédiaire (type 2) à foncée (type 3) renfermant des filons de quartz aurifere qui occupent des zones de eisaillement cassantes à déformables, orientées ver\ Ic nord-est. dans des roches sédimcntaires volcanoclastiques à coméenncs marines peu profondes des formations silunennes de Wawcig el d'Oak Bay. La proximilé de la limite faillée (faille du runsseau Sawyer) entre le terrane ordovicien de St. Croix, au nord-ouest et le bassin du Silurien au Dévonien inférieur de Mascarenc. au sud-est, a amené les zones du eisaillement à longer parallélement la structure régionale. Des éludes géochimiques des dykes du ruisseau East Branch révèlent que trois impulsions (composante riche en Fer. composante intermédiaire et composante riche en Mg) de magmas tholéutiques continentaux, allant de subalcalins à légèrement alcalms sont survenues dans un environnement transpressionnel pendant la période du Silurien inferieur au Dévonien infèrieur. Les vateurs positives de εNd lémoignent de leur provenance d'un manteau particllement appauri pendant la formation de failles et des phénomènes apparcntes à une distension Même les données géeochimiques (appaurassement en Fe et en Ti) revèlent unc affinité calcoalcaline du complexe intrusif proche de Bocabec. les valeurs de εNd et les configurations de diagrammes en araignée normalisées du manteau primitif sont analogues a celles des dykes du ruisseau East Branch Par contre, l'intrusion de Saint Stephen semble plus primitive avec une affinite mira-plaques allant de tholénlique à légèrcment alcaline Traduit par la rédaction

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Published

2001-10-01

How to Cite

Thorne, K. G., & Lentz, D. R. (2001). Geochemistry and petrogenesis of the East Branch Brook metagabbroic dykes in the Sawyer Brook fault zone, Clarence Stream gold prospect, southwestern New Brunswick. Atlantic Geoscience, 37(2/3). https://doi.org/10.4138/1978

Issue

Vol. 37 No. 2/3 (2001)

Section

Articles

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